Interesting question. There are quite a few words that you could use to convey the idea of her having left:

deserted, left, quit, defected, for example.

It's much more difficult to find a single word that conveys the ideas of 'leaving' and 'for good'.

Could any of the following work?

Ditched (us), bailed out (on us), cut loose and run, flown the coop, flown the nest (usually used to indicate children having grown up and left home), walked out on.

The best one-word option I can think of is to see if you can think of a famous literary character, and use her name as a verb. For instance, if you were trying to describe a girl who eloped with a lover, you might say she 'Jessica-d' / 'Jessicaed' / 'Jessica'd' as in Merchant of Venice.